Electric Charge

Question 1

static electricity is all about…

Answer 1

…charges which are NOT free to move. this causes them to build up in one place and it often ends with a spark or a shock when they do finally move.

Question 2

Like charges ______, opposite charges _____

Answer 2

1. repel
2. attract

these forces get weaker the further apart the 2 things are.

Question 3

what are conductors?

Answer 3

materials that conduct charge easily- a current flows easily through them.
usually metals

Question 4

what are insulators?

Answer 4

don’t conduct charge well so a current can’t flow eg plastic and rubber

Question 5

what is a common cause of static electricity?

Answer 5

FRICTION: when 2 insulating materials are rubbed together, electrons will be scraped off one and dumped on the other.

Question 6

can static charges occur on conductors too?

Answer 6

YES.

cars often get a static charge on the outside because they’ve gained or lost electrons from the air rushing past them as they travel at high speeds.

Question 7

how can a charged conductor be safely discharged?

Answer 7

• connecting it to earth with a metal strap. the electrons flow down the strap if charge is negative and up from the ground if charge is positive.

Question 8

as charge builds up… so does voltage.

Answer 8

1. as an electric charge builds on an isolated object, the voltage between the object and the earth- (at zero volts) increases.
2. if the voltage gets large enough, electrons can jump across the gap between the charged object and the earth- this is the spark.
3. they can also jump to any earthed conductor nearby
4. usually happens when the gap is fairly small (except lightning)

Question 9

suspending a charged rod practical

Answer 9

1. suspend a rod with a known charge on a thread.

2. see if there is repulsion or attraction when the rod you’re testing is brought close.

Question 10

polythene and acetate rods

Answer 10

polythene rod - rod becomes negatively charged and duster positively

acetate rod - rod positively charged and duster negatively

Question 11

Photocopier

Answer 11

1. image plate positively charged. image of what you’re copying is projected onto it.
2. whiter bits of what you’re copying make light fall onto the plate and the charge LEAKS away in these places.
3. the charges bits attract negatively charged black powder, which is transferred onto positively charged paper
4. the paper is heated so the powder sticks
5. photocopy is produced

Question 12

Inkjet printer

Answer 12

1. tiny droplets of ink are forced out of a fine nozzle making them electrically charges.
2. the droplets are deflected as they pass between two metal plates. a voltage is applied to the plates- one is negative and the other positive
3. droplets are attracted to plate with opposite charge and repelled from plate with same charge.
4. the size and direction of the voltage across each plate changes so each droplets is deflected to hit a different place on the paper.

Question 13

fuel pipes

Answer 13

1. as fuel flows out of a filler pipe static can build up
2. this can easily build to a spark, and in dusty or fumy places an explosion
3. the solution is to make the nozzles out of metal so the charge is conducted away instead of building up
4. it’s also good to have earthing straps between fuel tank and fuel pipe